1. FIELD OF THE INVENTION
The present invention relates to a process for producing coke. More particularly, it relates to a process for producing coke for a carbon artifact such as a graphite electrode or a carbon brush, particularly needle coke which is used in a large amount primarily as particulate carbon material for electrodes.
2. DISCUSSION OF BACKGROUND
Carbon artifacts such as graphite electrodes or carbon brushes are produced usually by pulverizing particles of carbon material such as various calcined coke including pitch coke and petroleum coke, noncalcined coke being an intermediate product thereof, natural graphite and/or carbon black, to adjust the particle size, then kneading it together with a binder such as binder pitch under heating, and molding it, followed by baking at a temperature of from 800.degree. to 1,300.degree. C., and if necessary, further followed by graphitization treatment at a temperature of from 2,500.degree. to 3,000.degree. C.
The coke used as particulate carbon material for the production of carbon artifacts, is produced usually by coking a starting material oil such as petroleum heavy oil, naturally produced gilsonite or coal tar pitch by a method such as a fluid coking method, a flex coking method or a delayed coking method. In recent years, the conditions under which carbon artifacts including graphite electrodes for steel making are used, have become severe, and the quality required for the carbon artifacts, particularly the heat shock resistance, tends to be high. Accordingly, it has been common to employ needle coke obtained by coking petroleum pitch or coal pitch from which quinoline insolubles have been removed, by the delayed coking method.
Recently, for the production of carbon artifacts, it has been common to employ a quick graphitization method, in which a carbon material is rapidly heat treated in a short time, for the purpose of energy saving. However, with a carbon artifact produced by using needle coke produced by a conventional method as carbon material, abnormal expansion or a puffing phenomenon is likely to appear during the quick graphitization, whereby cracks are likely to form, or if cracks do not form, the apparent specific gravity is likely to be small, whereby no adequate strength will be obtained.
A number of attempts have been made to suppress the puffing phenomenon during the quick graphitization treatment by adding various additives to the starting material oil. However, no adequate results have been obtained.
When the particulate carbon material used is other than needle coke, there will be no problem of puffing. However, in view of the severe condition under which the carbon artifact is used, a coke is desired which is capable of providing adequate strength to the carbon artifact when it is used as particulate carbon starting material for the production of the carbon molded production.